Interconnect Structure with Partial Sidewall Liner

ABSTRACT

An interconnect structure and techniques for fabrication thereof having a partial sidewall liner are provided. In one aspect, the interconnect structure includes: a substrate; a dielectric disposed on the substrate having at least one feature present therein; a barrier layer lining the at least one feature; a seed enhancement liner disposed over the barrier layer along sidewalls of the at least one feature, wherein the seed enhancement liner is present along only a middle portion of the sidewalls of the at least one feature; and at least one interconnect disposed within the at least one feature over the barrier layer and the seed enhancement liner.

FIELD OF THE INVENTION

The present invention relates to interconnect structures, and moreparticularly, to a copper (Cu) interconnect structure and techniques forfabrication thereof having a partial sidewall seed enhancement liner forvoid-free Cu fill without Cu loss at a top of the interconnect structureduring polishing.

BACKGROUND OF THE INVENTION

Interconnect structures in semiconductor device designs are typicallyformed using a damascene or dual damascene process that involves firstpatterning a feature(s) such as a trench (for metal lines) and/or a via(for conductive vias) in a dielectric, lining the features with adiffusion barrier, and then filling the features with a metal(s) such ascopper (Cu). As the size of the interconnect features shrinks, thebarrier thickness needs to be scaled down in order to maximize thecopper Cu volume. Doing so enables low line and via resistance. Scalingthe sidewall barrier thickness and coverage allows for the maximizationof Cu volume in the interconnects, and scaling barrier thickness at thevia bottom allows for the reduction of via resistance.

For void-free Cu fill at less than or equal to about 24 nanometer (nm)critical dimensions, an additional liner or seed enhancement layer (suchas ruthenium (Ru)) is deposited to prevent barrier exposure during Cuplating, especially on the feature sidewalls. Without a seed enhancementlayer, sidewall voids will form which lead to poor device performance.

However, the use of a Ru liner provides some notable fabricationchallenges. For instance, chemical-mechanical polishing (CMP) of Cuinterconnects containing a Ru liner is difficult. Specifically, thegalvanic corrosion of Cu during Ru CMP can result in Cu loss at a topinterface of the interconnect. Unfortunately, this Cu loss is a keycontributor to high line resistance which is undesirable.

Thus, techniques for forming void-free Cu interconnects with a high Cuvolume using a Ru liner but eliminating Cu volume loss during CMP wouldbe desirable.

SUMMARY OF THE INVENTION

The present invention provides a copper (Cu) interconnect structure andtechniques for fabrication thereof having a partial sidewall seedenhancement liner. In one aspect of the invention, an interconnectstructure is provided. The interconnect structure includes: a substrate;a dielectric disposed on the substrate having at least one featurepresent therein; a barrier layer lining the at least one feature; a seedenhancement liner disposed over the barrier layer along sidewalls of theat least one feature, wherein the seed enhancement liner is presentalong only a middle portion of the sidewalls of the at least onefeature; and at least one interconnect disposed within the at least onefeature over the barrier layer and the seed enhancement liner.

In another aspect of the invention, a method of forming an interconnectstructure is provided. The method includes: depositing a dielectric ontoa substrate; patterning at least one feature in the dielectric;depositing a barrier layer into and lining the at least one feature;forming a seed enhancement liner over the barrier layer along only amiddle portion of sidewalls of the at least one feature; and forming atleast one interconnect within the at least one feature over the barrierlayer and the seed enhancement liner.

A more complete understanding of the present invention, as well asfurther features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram illustrating the presentinterconnect structure according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional diagram illustrating a dielectric layerhaving been deposited on a substrate, and at least one feature havingbeen patterned in the dielectric layer according to an embodiment of thepresent invention;

FIG. 3 is a cross-sectional diagram illustrating a conformal barrierlayer having been deposited onto the dielectric layer and lining thefeatures according to an embodiment of the present invention;

FIG. 4 is a cross-sectional diagram illustrating a first fill havingbeen deposited into, and filling, the features over the barrier layeraccording to an embodiment of the present invention;

FIG. 5 is a cross-sectional diagram illustrating the first fill havingbeen recessed according to an embodiment of the present invention;

FIG. 6 is a cross-sectional diagram illustrating a conformal seedenhancement liner having been deposited onto the dielectric layer andinto the features over the barrier layer and the recessed first Cu fillaccording to an embodiment of the present invention;

FIG. 7 is a cross-sectional diagram illustrating a recess etch havingbeen used to remove the seed enhancement liner from horizontal surfaces,including along the top surface of the dielectric layer/barrier layerand from the first Cu fill at the bottom of the features according to anembodiment of the present invention;

FIG. 8 is a cross-sectional diagram illustrating a first Cu-containingseed layer having been deposited onto the dielectric layer and into thefeatures over the barrier layer and seed enhancement liner, lining thefeatures over the first Cu fill according to an embodiment of thepresent invention;

FIG. 9 is a cross-sectional diagram illustrating a second Cu fill havingbeen deposited into the features over the first Cu-containing seed layeraccording to an embodiment of the present invention;

FIG. 10 is a cross-sectional diagram illustrating the firstCu-containing seed layer and the second Cu fill having been recessedaccording to an embodiment of the present invention;

FIG. 11 is a cross-sectional diagram illustrating the seed enhancementliner having been recessed to the height of the (recessed) firstCu-containing seed layer/second Cu fill according to an embodiment ofthe present invention;

FIG. 12 is a cross-sectional diagram illustrating a second Cu-containingseed layer having been deposited into the features over the (recessed)first Cu-containing seed layer/second Cu fill and the (recessed) seedenhancement liner according to an embodiment of the present invention;

FIG. 13 is a cross-sectional diagram illustrating a third Cu fill havingbeen deposited into the features over the second Cu-containing seedlayer according to an embodiment of the present invention; and

FIG. 14 is a cross-sectional diagram illustrating the secondCu-containing seed layer and the third Cu fill having been polishedusing a process such as chemical-mechanical polishing (CMP) according toan embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Provided herein are void-free copper (Cu) interconnect structures with ahigh Cu volume and techniques for fabrication thereof that leverage thebenefits of a seed enhancement liner where needed (in terms of void-freeCu fill), while maintaining a high Cu volume ratio in the trench andeliminating Cu volume loss during chemical-mechanical polishing (CMP) toenable reliable, low line resistance Cu interconnects. Advantageously,the present techniques provide lower overall line resistance (due torelative higher Cu volume), as well as a lower via resistance (due tothe absence of a bottom liner, and use of the largest contact areaavailable).

FIG. 1 is a diagram illustrating the unique design of the presentinterconnect structure. Namely, as shown in FIG. 1, an interconnectstructure 10 includes a dielectric 14, disposed on a substrate 12,having features 16 present therein. In FIG. 1, dotted lines are used toillustrate the outlines of features 16. By way of example only, features16 can include trenches and/or vias. It is notable that the presenttechniques are applicable to interconnect structure designs includingany number of features 16, including those having a single feature 16.

According to an exemplary embodiment, substrate 12 is a bulksemiconductor wafer, such as a bulk silicon (Si), bulk germanium (Ge),bulk silicon germanium (SiGe) and/or bulk III-V semiconductor wafer.Alternatively, substrate 12 can be a semiconductor-on-insulator (SOI)wafer. A SOI wafer includes a SOI layer separated from an underlyingsubstrate by a buried insulator. When the buried insulator is an oxideit is referred to herein as a buried oxide or BOX. The SOI layer caninclude any suitable semiconductor, such as Si, Ge, SiGe, and/or a III-Vsemiconductor. Substrate 12 may already have pre-built structures (notshown) such as transistors, diodes, capacitors, resistors, isolationregions (e.g., shallow trench isolation (STI) regions), interconnects,wiring, etc.

Suitable materials for dielectric layer 14 include, but are not limitedto, oxide low-κ materials such as silicon oxide (SiOx) and/or oxideultralow-κ interlayer dielectric (ULK-ILD) materials, e.g., having adielectric constant κ of less than 2.7. By comparison, silicon dioxide(SiO₂) has a dielectric constant κ value of 3.9. Suitable ultralow-κdielectric materials include, but are not limited to, porousorganosilicate glass (pSiCOH). A process such as chemical vapordeposition (CVD), atomic layer deposition (ALD) or physical vapordeposition (PVD) can be employed to deposit the dielectric layer 14 ontothe substrate 12. According to an exemplary embodiment, the dielectriclayer 14 has a thickness of from about 10 nanometers (nm) to about 400nm and ranges therebetween.

A barrier layer 18 is present lining the features 16. Use of such abarrier layer 18 helps to prevent diffusion of the interconnect Cu (seebelow) into the surrounding dielectric 14. Suitable materials forbarrier layer 18 include, but are not limited to, tantalum (Ta),tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN) and/ortungsten nitride (WN). According to an exemplary embodiment, barrierlayer 18 has a thickness of from about 1 nm to about 5 nm and rangestherebetween.

A seed enhancement liner 20 is disposed over the barrier layer alongopposite sidewalls of the features 16. Suitable materials for the seedenhancement liner 20 include, but are not limited to, ruthenium (Ru),rhodium (Rh) and/or palladium (Pd). According to an exemplaryembodiment, the seed enhancement liner 20 has a thickness of from about2 nm to about 5 nm and ranges therebetween.

As shown in FIG. 1, the seed enhancement liner 20 is present along onlya middle portion of those sidewalls of the features 16. Specifically,the seed enhancement liner 20 does not touch the top or the bottom offeatures 16, i.e., the seed enhancement liner 20 is absent from thesidewalls of the features 16 at the top and bottom of features 16.

More specifically, according to an exemplary embodiment, the middleportion of the sidewalls of the features 16 along which the seedenhancement liner 20 is present is less than or equal to about 60% of atotal sidewall height H of features 16, for example, the middle portionof the sidewalls of the features 16 along which the seed enhancementliner 20 is present is from about 50% to about 60% and rangestherebetween of the total sidewall height H of features 16 (see FIG. 1).

As will be described in detail below, the absence of the seedenhancement liner 20 at the top of the features 16 advantageously avoidsgalvanic corrosion of the Cu at the top of the interconnects duringchemical-mechanical polishing (CMP). Galvanic corrosion can lead to Culoss at the top of the interconnect which is a key contributor to highline resistance.

Interconnects 22 are disposed within the features 16 over the barrierlayer 18 and seed enhancement liner 20. See FIG. 1. According to anexemplary embodiment, the interconnects are formed from Cu. As will bedescribed in detail below, according to an exemplary embodiment, aseries of seed layers and electroplated Cu collectively form theinterconnects 22. However, for clarity, the interfaces between thesevarious layers are not shown in the depiction presented in FIG. 1.

As shown in FIG. 1, the present interconnects 22 have a uniqueconfiguration. Notably, due to the absence of the seed enhancement liner20 at the top of the features 16, Cu loss during CMP after the finalplated Cu (see below) is avoided, resulting in a top surface of theinterconnects 22 being coplanar with a top surface of the dielectric 14.See FIG. 1.

Further, since the seed enhancement liner 20 is present along only amiddle portion of those sidewalls of the features 16, the interconnects22 have a unique flanged top and bottom. For instance, as shown in FIG.1, the top and the bottom of interconnects 22 have a width W1, while amiddle of the interconnects 22 has a width W2, wherein W1>W2.

An exemplary methodology for forming an interconnect structure inaccordance with the present techniques is now described by way ofreference to FIGS. 2-14. As shown in FIG. 2, the process begins with thedeposition of a dielectric layer 204 on a substrate 202, and thepatterning of at least one feature 206 in the dielectric layer 204.

As above, substrate 202 can be a bulk semiconductor wafer, such as abulk Si, bulk Ge, bulk SiGe and/or bulk III-V semiconductor wafer.Alternatively, substrate 202 is a SOI wafer, where the SOI layerincludes a semiconductor, such as Si, Ge, SiGe, and/or a III-Vsemiconductor. Substrate 202 may already have pre-built structures (notshown) such as transistors, diodes, capacitors, resistors, isolationregions (e.g., shallow trench isolation (STI) regions), interconnects,wiring, etc.

As provided above, suitable materials for dielectric layer 204 include,but are not limited to, oxide low-κ materials such as SiOx and/or oxideULK-ILD materials, e.g., having a dielectric constant κ of less than2.7, such as pSiCOH. A process such as chemical vapor deposition (CVD),atomic layer deposition (ALD) or physical vapor deposition (PVD) can beemployed to deposit the dielectric layer 204 onto the substrate 202.According to an exemplary embodiment, the dielectric layer 204 has athickness of from about 10 nm to about 400 nm and ranges therebetween.

By way of example only, features 206 include trenches and/or vias.Lithography and etching processes can be employed to pattern thefeatures 206 in dielectric layer 204. With standard lithography andetching processes, a lithographic stack (not shown), e.g.,photoresist/organic planarizing layer (OPL)/anti-reflective coating(ARC), is used to pattern a hardmask (not shown). The pattern from thehardmask is then transferred to the underlying layer(s), i.e., in thiscase dielectric layer 204. The hardmask is then removed. According to anexemplary embodiment, a directional (anisotropic) etching process suchas reactive ion etching (RIE) is employed for the feature etch.Alternatively, the hardmask can be formed by other suitable techniques,including but not limited to, sidewall image transfer (SIT),self-aligned double patterning (SADP), self-aligned quadruple patterning(SAQP), and other self-aligned multiple patterning (SAMP).

In the present example, the features 206 as patterned extend onlypartway through the dielectric layer 204. Namely, a portion of thedielectric layer 204 remains at the bottoms of features 206. Thisremaining portion of the dielectric layer 204 at the bottom of thefeatures 206 will serve to insulate the interconnect structures thatwill be formed in features 206 from the underlying substrate 202 (seebelow). As will be apparent from the description that follows,metallization of the features 206 will be used to form metal linesand/or conductive vias when the features 206 are trenches and/or vias,respectively.

A conformal barrier layer 302 is then deposited onto dielectric layer204 and lining features 206. See FIG. 3. Use of such a barrier layer 302helps to prevent diffusion of the interconnect Cu (see below) into thesurrounding dielectric layer 204. As provided above, suitable materialsfor barrier layer 302 include, but are not limited to, Ta, TaN, Ti, TiNand/or WN. A process such as CVD, ALD or PVD can be employed to depositthe barrier layer 302. According to an exemplary embodiment, barrierlayer 302 has a thickness of from about 1 nm to about 5 nm and rangestherebetween. Additionally, a seed layer (not shown) can be depositedinto and lining the features 206 over the barrier layer 302 prior to Cudeposition. A seed layer facilitates plating of the Cu into the features206. The use of a seed layer is described in detail below.

A Cu fill 402 is then deposited into, and filling, the features 206 overbarrier layer 302. See FIG. 4. A process such as sputtering, evaporationor electrochemical plating can be employed to deposit the Cu fill 402into the features 206. Following deposition, the Cu overburden isremoved using a process such as chemical mechanical polishing (CMP).According to an exemplary embodiment, as deposited, Cu fill 402 has athickness T1 of from about 30 nm to about 50 nm and ranges therebetween.

As shown in FIG. 4, during the Cu fill, voids can form in Cu layer 402such as is shown along the sidewalls of the features 206. These voidscan form where the barrier layer 302 is thinnest, such as along thesidewalls of features 206. For instance, due to poor step coverage, inpractice the barrier layer 302 deposited along the middle portion of thesidewalls of features 206 can in fact be slightly thinner than thebarrier layer 302 at the bottom and top of features 206. See magnifiedview 404. It is at these thinner regions of barrier layer 302 that voidscan form. See, for example, Y. L. Hsu et al., “Failure Mechanism ofElectromigration in Via Sidewall for Copper Dual DamasceneInterconnection,” Journal of the Electrochemical Society, 153 (8)G782-G786 (June 2006), the contents of which are incorporated byreference as if fully set forth herein. This problem is especiallyprevalent in small features where the overall barrier thickness isscaled down in order to maximize the copper Cu volume to enable low lineand via resistance.

The Cu fill 402 is then recessed. See FIG. 5. By way of example only, Cufill 402 can be recessed at this stage using a wet chemical etchingprocess such as NH₄OH/H₂O₂. The recessed Cu is now given referencenumeral 402 a. According to an exemplary embodiment, this recess etchstep leaves Cu fill 402 a having only a thickness T2 of from about 5 nmto about 20 nm and ranges therebetween. Doing so ensures that the voidsalong the sidewalls of features 206 (see FIG. 4) are removed. To look atit another way, Cu fill 402 a is recessed below the voids such that,following the recess etch, no voids remain along the sidewalls offeatures 206.

A conformal seed enhancement liner 602 is next deposited onto dielectriclayer 204 and into the features 206 over the barrier layer 302 andrecessed Cu fill 402 a. See FIG. 6. As provided above, suitablematerials for the seed enhancement liner 602 include, but are notlimited to, Ru, Rh and/or Pd. A process such as CVD, ALD or PVD can beemployed to deposit the seed enhancement liner 602. According to anexemplary embodiment, the seed enhancement liner 602 has a thickness offrom about 2 nm to about 5 nm and ranges therebetween. As deposited, theseed enhancement liner 602 is present at the top and bottom, as well asalong the sidewalls of features 206. However, the goal will be toultimately remove all but the portion of the seed enhancement liner 602along the middle portion of the sidewalls of features 206, i.e., whatwill remain of the seed enhancement liner 602 will touch neither the topnor the bottom of features 206.

A recess etch is then used to remove the seed enhancement liner 602 fromhorizontal surfaces, including along the top surface of dielectric layer204/barrier layer 302 and from Cu fill 402 a at the bottom of features206. See FIG. 7. As shown in FIG. 7, seed enhancement liner 602 is nowpresent along only the sidewalls of features 206. According to anexemplary embodiment, the recess etch is performed using a directional(anisotropic) etching process such as RIE.

A Cu-containing seed layer 802 is then deposited onto dielectric layer204 and into the features 206 over barrier layer 302 and seedenhancement liner 602, lining the features 206 over Cu fill 402 a. SeeFIG. 8. The use of seed layer 802 will facilitate plating of Cu fill 902(see below) into the features 206. Seed layer 802 can be formed from Cualone or in combination with one or more other elements such as aluminum(Al) and/or manganese (Mn), i.e., a CuAl or CuMn alloy. A process suchas CVD, ALD or PVD can be employed to deposit the seed layer 802.Advantageously, seed enhancement liner 602 enhances adherence of theseed layer 802 along the sidewalls of features 206, thereby ensuringthat the seed layer 802 fully lines the features 206 without having anyvoids.

Cu fill 902 is then deposited into the features 206 over seed layer 802.See FIG. 9. The terms “first” and “second” may also be used herein whenreferring to Cu fill 402 and Cu fill 902, respectively. As shown in FIG.9, Cu fill 802 overfills features 206. According to an exemplaryembodiment, Cu fill 902 is deposited into features 206 using a processsuch as electrochemical plating. Following plating, an anneal ispreferably performed to increase the grain size of the Cu fill 902through grain regrowth, and to eliminate voids. According to anexemplary embodiment, this anneal is performed at a temperature of fromabout 200° C. to about 400° C. and ranges therebetween.

Seed layer 802 and Cu fill 902 are then recessed. See FIG. 10. By way ofexample only, seed layer 802/Cu fill 902 can be recessed using anetching process such as CMP with over-polishing or wet chemical etching.According to an exemplary embodiment, the seed layer 802/Cu fill 902 arerecessed to approximately the mid-height of features 206. For instance,at this point in the process, if features 206 have a height h (see FIG.10), then the seed layer 802/Cu fill 902 are recessed to about ½h. Asshown in FIG. 10, following the recess etch the seed enhancement liner602 is still present along the sidewall at the top of features 206.However, a recess etch of the seed enhancement liner 602 will next beperformed.

Namely, as shown in FIG. 11, the seed enhancement liner 602 is nextrecessed to the height of (recessed) seed layer 802/Cu fill 902, e.g.,about ½h (see above). According to an exemplary embodiment, the seedenhancement liner 602 is recessed using an etching process such as wetchemical etching. Notably, the seed enhancement liner 602 is now presentalong only the middle portion of the sidewalls of features 206. In otherwords, what remains of the seed enhancement liner 602 following therecess etch will touch neither the top nor the bottom of features 206,i.e., the seed enhancement liner 602 is absent from both the top and thebottom of features 206. Removal of the seed enhancement liner 602 fromthe top of features 206 advantageously avoids galvanic corrosion of thecopper during a subsequent CMP step (see below). As provided above,galvanic corrosion can lead to copper loss at the top of theinterconnect which is a key contributor to high line resistance.

A copper oxide reduction is then preferably performed to convert anycopper oxide on the surface of seed layer 802/Cu fill 902 to metalliccopper. According to an exemplary embodiment, this copper oxidereduction is performed using a pure hydrogen (H₂) plasma or a reactiveplasma clean process containing hydrogen/helium (H₂/He) or hydrogen/neon(H₂/Ne) gas mixtures. Following the copper oxide reduction, aCu-containing seed layer 1202 is deposited into features 206 over(recessed) seed layer 802/Cu fill 902 and (recessed) seed enhancementliner 602. See FIG. 12. For clarity, the terms “first” and “second” mayalso be used herein when referring to seed layer 802 and seed layer1202.

As with seed layer 802, the use of seed layer 1202 will facilitateplating of Cu 1302 (see below) into the features 206. However, in thiscase seed layer 1202 is being deposited into much lower aspect ratiofeatures 206 than seed layer 802. Namely, the bottom ½h (see above) ofthe features 206 are already filled by (recessed) seed layer 802/Cu fill902. Thus, even though the seed enhancement liner 602 is no longerpresent along the sidewalls at the tops of features 206, full coverageof seed layer 1202 without voids along the lower aspect ratio features206 can be easily achieved. Seed layer 1202 can be formed from Cu aloneor in combination with one or more other elements such as Al and/or Mn,i.e., a CuAl or CuMn alloy. A process such as CVD, ALD or PVD can beemployed to deposit the seed layer 1202.

A Cu fill 1302 is then deposited into the features 206 over seed layer1202. See FIG. 13. For clarity, the term “third” may also be used hereinwhen referring to Cu fill 1302, so as to distinguish it from first Cufill 402 and second Cu fill 902. As shown in FIG. 13, Cu fill 1302overfills features 206. According to an exemplary embodiment, Cu fill1302 is deposited into features 206 using a process such aselectrochemical plating. Following plating, an anneal is preferablyperformed to increase the grain size of the Cu fill 1302 through grainregrowth, and to eliminate voids. According to an exemplary embodiment,this anneal is performed at a temperature of from about 200° C. to about400° C. and ranges therebetween.

Seed layer 1202 and Cu fill 1302 are then polished using a process suchas CMP. See FIG. 14. Advantageously, the seed enhancement liner 602 isabsent from the sidewalls at the tops of features 206. Thus, thispolishing occurs only at an interface between seed layer 1202/Cu fill1302 and barrier layer 302. To look at it another way, there is no seedenhancement liner 602 (e.g., Ru, Rh and/or Pd) present at thisinterface. Accordingly, the galvanic corrosion of Cu during CMP ofmaterials such as Ru, Rh and/or Pd can be avoided altogether thuspreventing Cu loss at a top interface of the interconnect.

Cu fill 402 a, seed layer 802, Cu fill 902, seed layer 1202 and Cu fill1302 collectively form interconnects 1402 in features 206. It is notablethat, in FIG. 1 (described above), the interfaces between these variouslayers were omitted for the purpose of clarity. However, the structuresshown in FIG. 1 and FIG. 14 have the same configuration, dimensions,etc. and thus are functionally identical. As such, the same designationsof sidewall height H/H′, width W1/W1′, W2/W2′, etc. are used in bothFIG. 1 and FIG. 14.

As shown in FIG. 14, the present process results in a uniqueinterconnect structure. Namely, the seed enhancement liner 602 ispresent only where needed, i.e., along the middle portion of thesidewalls of the features 206. This is what is referred to herein as a‘partial sidewall liner.’ According to an exemplary embodiment, themiddle portion of the sidewalls of the features 206 along which the seedenhancement liner 602 is present is less than or equal to about 60% ofthe total sidewall height H′ of features 206, for example, the middleportion of the sidewalls of the features 206 along which the seedenhancement liner 602 is present is from about 50% to about 60% andranges therebetween of the total sidewall height H′ of the features 206(see FIG. 14). Thus, by way of a non-limiting example only, if theheight H′ of features 206 is 20 nm, then the middle portion of thesidewalls of features 206 along which the seed enhancement liner 602 isdisposed is less than or equal to about 12 nm, e.g., from about 10 nm toabout 12 nm and ranges therebetween

Due to the absence of the seed enhancement liner 602 at the top of thefeatures 206, Cu loss during the CMP is avoided, resulting in a topsurface of the interconnects 1402 being coplanar with a top surface ofthe dielectric 204. See FIG. 14.

Further, since the seed enhancement liner 602 is present along only amiddle portion of those sidewalls of the features 206, the interconnects1402 have a unique flanged top and bottom. For instance, as shown inFIG. 14, the top and the bottom of interconnects 1402 have a width W1′,while a middle of the interconnects 1402 has a width W2′, whereinW1′>W2′.

Although illustrative embodiments of the present invention have beendescribed herein, it is to be understood that the invention is notlimited to those precise embodiments, and that various other changes andmodifications may be made by one skilled in the art without departingfrom the scope of the invention.

What is claimed is:
 1. An interconnect structure, comprising: asubstrate; a dielectric disposed on the substrate having at least onefeature present therein; a barrier layer lining the at least onefeature; a seed enhancement liner disposed over the barrier layer alongsidewalls of the at least one feature, wherein the seed enhancementliner is present along only a middle portion of the sidewalls of the atleast one feature; and at least one interconnect disposed within the atleast one feature over the barrier layer and the seed enhancement liner.2. The interconnect structure of claim 1, wherein the at least onefeatures is selected from the group consisting of: a trench, a via, andcombinations thereof.
 3. The interconnect structure of claim 1, whereinthe barrier layer comprises a material selected from the groupconsisting of: tantalum (Ta), tantalum nitride (TaN), titanium (Ti),titanium nitride (TiN), tungsten nitride (WN), and combinations thereof.4. The interconnect structure of claim 1, wherein the seed enhancementliner comprises a material selected from the group consisting of:ruthenium (Ru), rhodium (Rh), palladium (Pd), and combinations thereof.5. The interconnect structure of claim 1, wherein the seed enhancementliner is absent from the sidewalls of the at least one feature at a topand at a bottom of the at least one feature.
 6. The interconnectstructure of claim 1, wherein the at least one interconnect comprisescopper (Cu).
 7. The interconnect structure of claim 1, wherein a topsurface of the at least one interconnect is coplanar with a top surfaceof the dielectric.
 8. The interconnect structure of claim 1, wherein theat least one interconnect has a flanged top and bottom with the top andthe bottom of the at least one interconnect having a width W1 and amiddle of the at least one interconnect having a width W2, and whereinW1>W2.
 9. The interconnect structure of claim 1, wherein the middleportion of the sidewalls of the at least one feature along which theseed enhancement liner is present comprises less than or equal to about60% of a total sidewall height Hof the at least one feature.
 10. Theinterconnect structure of claim 1, wherein the middle portion of thesidewalls of the at least one feature along which the seed enhancementliner is present comprises from about 50% to about 60% and rangestherebetween of a total sidewall height H of the at least one feature.11. The interconnect structure of claim 1, wherein the at least oneinterconnect comprises a metal line, a conductive via or combinationsthereof.
 12. A method of forming an interconnect structure, the methodcomprising the steps of: depositing a dielectric onto a substrate;patterning at least one feature in the dielectric; depositing a barrierlayer into and lining the at least one feature; forming a seedenhancement liner over the barrier layer along only a middle portion ofsidewalls of the at least one feature; and forming at least oneinterconnect within the at least one feature over the barrier layer andthe seed enhancement liner.
 13. The method of claim 12, furthercomprising the steps of: depositing a first copper (Cu) fill into the atleast one feature over the barrier layer; recessing the first Cu fill toform a recessed Cu fill; depositing a seed enhancement liner into the atleast one feature over the barrier layer and the recessed Cu fill;depositing a first Cu-containing seed layer into the at least onefeature over the seed enhancement liner, the barrier layer and therecessed Cu fill; depositing a second Cu fill into the at least onefeature over the first Cu-containing seed layer; recessing the firstCu-containing seed layer and the second Cu fill; and recessing the seedenhancement liner such that the seed enhancement liner is absent from atop of the at least one feature.
 14. The method of claim 13, furthercomprising the steps of: depositing a second Cu-containing seed layerinto the at least one feature over the first Cu-containing seed layer,the second Cu fill, and the seed enhancement liner that have beenrecessed; depositing a third Cu fill into the at least one feature overthe second Cu-containing seed layer; polishing the third Cu fill and thesecond Cu-containing seed layer, wherein the recessed Cu fill, the firstCu-containing seed layer, the second Cu fill, the second Cu-containingseed layer and the third Cu fill collectively form the at least oneinterconnect disposed within the at least one feature.
 15. The method ofclaim 13, wherein, following the polishing step, a top surface of the atleast one interconnect is coplanar with a top surface of the dielectric.16. The method of claim 12, wherein the at least one interconnect has aflanged top and bottom with the top and the bottom of the at least oneinterconnect having a width W1 and a middle of the at least oneinterconnect having a width W2, and wherein W1>W2.
 17. The method ofclaim 12, wherein the middle portion of the sidewalls of the at leastone feature along which the seed enhancement liner is present comprisesfrom about 50% to about 60% and ranges therebetween of a total sidewallheight H of the at least one feature.
 18. The method of claim 12,wherein the at least one features is selected from the group consistingof: a trench, a via, and combinations thereof.
 19. The method of claim12, wherein the barrier layer comprises a material selected from thegroup consisting of: Ta, TaN, Ti, TiN, WN, and combinations thereof. 20.The method of claim 12, wherein the seed enhancement liner comprises amaterial selected from the group consisting of: Ru, Rh, Pd, andcombinations thereof.